Abstract

The superior resolution of optical coherence tomography (OCT) with respect to alternative imaging modalities makes it highly attractive, and some of its applications are already in extensive clinical use. However, one of the major limitations of OCT is that the tomographic picture it generates is depth-limited to approximately 1 mm in most biological tissues. This is mainly due to the spatially turbulent nature of the tissue, which leads to scattering. Moreover, this technique is extremely sensitive to temporal variations in the medium. We show that insensitivity to temporal and spatial turbulence may be gained by replacing the linear detector with an ultrasensitive two-photon detector. These results have striking implications on the attainable penetration depth of optical imaging and on its sensitivity to sample motion.

P. van der Zee, “Measurement and modelling of the optical properties of human tissue in the near infrared,” Ph. D. dissertation (Department of Medical Physics and Bioengineering, University College London, 1993).

Twiss, R. Q.

van der Zee, P.

P. van der Zee, “Measurement and modelling of the optical properties of human tissue in the near infrared,” Ph. D. dissertation (Department of Medical Physics and Bioengineering, University College London, 1993).

Technometrics (1)

Other (4)

P. van der Zee, “Measurement and modelling of the optical properties of human tissue in the near infrared,” Ph. D. dissertation (Department of Medical Physics and Bioengineering, University College London, 1993).

Figures (6)

(a) Schematics of TPA in a semiconductor direct-bandgap material (CB, conduction band; VB, valence band). (b) SO-OCT setup: a chaotic NIR source enters a Michelson interferometer through a λ>1μm filter and is detected at the output by TPA in a GaAs PMT. A phase modulator located before the sample generates temporal phase variations.

(a) First-order OCT measurement (blue) of a single reflector resulting in a high-frequency carrier multiplied by an exponentially decaying envelope, in addition to a constant background (green). (b) SO-OCT measurement of a single reflector resulting in frequency content around DC (green) in addition to high-frequency terms. The inset is the spectrum of the source. (c) Standard first-order OCT through temporally variant phase. The inset is a schematic of one-photon absorption. (d) SO-OCT through temporally variant phase. The inset is a schematic of TPA.

SO-OCT measurement of a single reflector with a λ/4 waveplate located before the sample, generating nearly orthogonal polarizations and therefore reduced visibility of the fringes only. The inset is a schematic of the setup.

Value of the peak of the interferogram’s envelope in first- and second-order OCT for imaging through turbid media as a function of depth [Eqs. (4) and (5)] for L0=4μm, 〈δn2〉=0.012, and a source of wavelength 1.3 μm and coherence time τc=100fs. The inset visualizes the frequency content of the two modalities along with the frequency response of the low-pass filter (LPF) caused by the phase variations.